Exposures to chemical migrating from Superfund sites are oftentimes comprised of exposures to complex mixtures. This is true for both human and wildlife exposures. The thrust of this project is to perform in-depth, quantitative analyses of the single and combined effects of selected Superfund chemicals on reproduction and growth in the common estuarine fish, the killifish (Fundulus heteroclitus). These chemicals will represent three mechanisms of action potentially related to reproductive and development effects: aryl hydrocarbon receptor-mediated, sex steroid hormone receptor-mediated, and oxidative stress. The principle goal of this project is to develop a biomarker-based strategy for assessing exposures to and reproductive/developmental effects of Superfund effects of Superfund chemicals in aquatic sentinel species that will be robust in the context of multiple exposures. The specific aims of this project are: 1) To quantify the effects of selected Superfund chemicals, singly and in combination, on reproduction and development in Fundulus heteroclitus (Fundulus). 2) To determine the ability of selected compounds to undergo maternal transfer to oocytes. 3) To establish correlations among developmental toxicities and mechanism-based biomarkers. 4) To determine the utility of mechanism-based biomarkers and broader indices of cellular effect to predict associated reproductive/developmental effects of multiple chemical exposure. 5) To develop a biomarker-based strategy for assessing exposures to and reproductive/developmental effects of Superfund contaminants that is robust in multiple exposure scenarios. 6) To apply this strategy to sediments collected from four Superfund sites.